Los Alamos

Underground tests of nuclear weapons were halted during 1992, and the Accelerated Strategic Computing Initiative (ASCI) was implemented in 1995 to develop simulation-based confidence in virtual testing and prototyping. This required a collaboration between SGI, which develops the high-performance computing applications environment required for weapons simulations of this scale, and Los Alamos National Laboratory (LANL) which develop large, complex models that push the demands of the data center.

Los Alamos is one of three U.S. Department of Energy (DOE) laboratories that are developing simulation capabilities in support of the program established in 1995. The ASCI program is a critical element behind a shift from test-based confidence to simulation-based confidence for performance, safety, engineering, and reliability assessment of the aging U.S. nuclear weapons stockpile.

Of particular interest is the dynamic response of components and materials under STS conditions of high-strain rate, impact, shock compression, and other types of dynamic loading. Dynamic response is a topic of considerable complexity that requires fundamental knowledge of material properties and mechanical response, not only at vastly different length and time scales, but also in the coupling of these scales.

The explicit finite element analysis software application Abaqus/Explicit was used to simulate 15 milliseconds of weapon response time after the event of a drop impact with the ground. More than 15,000 10-hour Abaqus/Explicit simulations were executed across the ASCI Blue Mountain system.

The Abaqus/Explicit simulation represents the largest utilization of computing resources within 72 hours for an engineering simulation. The usefulness of a combined probabilistic structural analysis and engineering sensitivity technique was demonstrated. This approach was considered by LANL to provide more engineering insight than large, million-FE models that may be executed only a few times. A single weapons model for the simulation contained only 30,000 finite elements.